1. Field of the Invention
The present invention relates generally to lens barrels, and more particularly, to a lens barrel, which allows smooth adjustment and ensures accurate positioning.
2. Description of the Related Art
FIG. 1 shows a conventional lens barrel for holding lenses therein. The lens barrel comprises a body 1 and an external thread 2 continuously spirally extending around the periphery of the body 1 for allowing fastening of the lens barrel to the internal thread of a camera's socket. The lens barrel can be rotated clockwise and counterclockwise, resulting in an axial movement relative to the socket to adjust the distance between the barrel and the image sensor in the camera for lens focusing.
However, because the external thread 2 is continuously spirally extending around the whole area of the periphery of the body 1, the external thread 2 is in full contact with the internal thread of the socket after engagement of the lens barrel in the socket. When adjusting the focus of the lens, a great friction is produced between the lens barrel and the socket. Therefore, the user must employ much effort to do the focusing adjustment.
There is known a lens barrel in which an axial plane cut through the external thread to reduce contact area between the lens barrel and the matching socket and to allow adjustment of focus with less effort. However, the axial plane interrupts the external thread, lowering the functioning of the external thread in guiding spiral rotation of the lens barrel into the matching socket and in positioning the lens barrel in the matching socket. In addition, this design may result in the light-leaking problem.